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high micorns

Ok guys, I will start by saying forgive me if this seems like a diy question. I have been out of the hvac field for 6 years and back in it for about 8 months. Im just trying to get back up to speed.
I was hooking up an older rheem unit today (homeowner had some landscaping done over winter so they had it in a basment for awhile) and i put a new dryer on it and re brazed the line set. I pumped 368 lbs of nitrogen in it to check my welds and let it sit for about 4 1/2 hours while i went to check on another customer. when i got back it was still on 368 lbs of pressure, so i pumped it down to 430 microns, when i turned the pump off the microns never restabilzed and within 20 mins was back up to 1500 microns. Normally i would say there was a leak somwhere in the system. so i pumped it back up with nitrogen and checked all the welds and all around the system for leaks, never even got a small bubble. re-pumped it back down to 450 microns, and within 20 mins again it was back to 1500 and climbing. Anyone have any ideas of whats going on? All help is greatly appreciated.

yeah, thats kinda what microns tell you, how much moisture is in the system. Most of the time after you pump it down you kinda expect a rise right when you turn off the pump but then the microns usually stabilize around a number and don't go much higher or lower than that. this one never stabilized, but it doesn't appear to be leaking either? thanks

wow, you guys are fast, you posted that before i could reply to the first one. Tomorrow when i get back out there ill change the oil in the pump, and let it pump for a few hours then. I appriciate it guys!! I don't remeber ever having to let it run that long before though.... I really need to stop jumping in and out of this field.. lol

Well then.
Just to double check, make sure you can pull a vac on your vacuum setup then. It's the little things that get us!

Like one time the 1/4" ftg that I had hooked up to the nitrogen when press. testing... of course I valved it off for the pressure test... but then I hooked it up to the micorn gauge and it had a leak of course.

lol, I once turned a suction line on a 410 unit into a small flame thrower... I would tell you what happened but you can probably guess... I think my vacuum pump is working fun cuase it doesn't have a problem getting 29.9, and it does drop the microns... but its a" just in case" thing... Ill let you know how it goes...